The present invention refers to an assembly for controlling the gas flow in a plasma spraying apparatus that comprises a treatment chamber and a plasma spraying device located in the interior of the treatment chamber.
For plasma coating of substrates, in most cases a plasma spraying apparatus is used that comprises a treatment chamber in the interior of which an atmosphere is created that is most suitable for a particular coating operation. Thereby, a plasma jet is generated by means of a plasmatron. In that plasma jet, the coating material to be applied to the surface of a substrate is molten. The plasma jet can reach a very high velocity, up to the ultrasonic region. However, in the interior of the treatment chamber, a gas flow is created during the operation of the plasmatron, particularly caused by the plasma jet. Such a gas flow can have a negative influence on the purity of the surface of the substrate as well as on the quality of the coating applied to the surface of the substrate.
The negative effect of such a gas flow in the interior of the treatment chamber is that loose deposits as dust, coating powder, spraying material residues and the like are whirled off the walls of the treatment chamber. Thereby, these deposits can reach the surface of the substrate to be coated and contaminate it. Moreover, whirled deposits can displace into the plasma jet and are entrained therewith. In the interior of the plasma jet, those impurities are heated and partially molten such that they are, together with the real coating material, applied to the surface of the substrate. It is understood, one the one hand, that a contamination of the surface of a substrate has a negative effect on the adhesion of the coating to be applied, and, on the other hand, that those impurities molten in the plasma jet influence the quality of the coating applied to the surface of the substrate to the worse.
It is therefore an object of the invention to provide a plasma spraying assembly for treating the surfaces of substrates by means of which the adhesion and the quality of the coating applied to the surfaces of the substrates is substantially improved.
To meet these and other objects, the present invention provides a plasma spraying assembly for treating the surfaces of substrates, comprising a treatment chamber, a vacuum pump operatively connected to the treatment chamber and adapted to create a subatmospheric pressure in the interior of the treatment chamber, and a plasma spraying device mounted in the interior of the treatment chamber.
Further, there is provided an assembly for controlling the gas flow in the interior of the treatment chamber, comprising a deflecting device located at least partially in the interior of the treatment chamber. The deflecting device includes a plurality of deflecting elements that are adapted to interfere with a gas flow in the interior of the treatment chamber.
In a preferred embodiment, the assembly for controlling the gas flow in the interior of the treatment chamber includes a collecting shaft located next to the treatment chamber and communicating therewith, whereby a basic element is located in the transition area between the treatment chamber and the collecting shaft. The basic element is provided with first baffle members and a passage for a gas exchange between the treatment chamber and the collecting shaft. A deflection element having essentially conical shape towers at least partially into the passage provided in the basic element.